1. Field of the Invention
The present invention rebates to a method of and a device for controlling the feeding of sheets one by one, of a type wherein when a plurality of sheets attracted under suction by a suction pad is detected, sheet feeding motion of the suction pad is changed, thereby making it possible to prevent the plurality of sheets from being fed simultaneously.
2. Description of the Related Art
In a conventional sheet feeding device, an uppermost sheet of stacked sheets, for example, stacked photographic light-sensitive mediums, is attracted under suction by a suction pad communicating with a vacuum source to be fed to a predetermined position. More specifically, sheets, for example, photographic light-sensitive mediums (e.g., an X-ray film and graphic art films, etc.), are taken out one by one from a supply magazine in which the sheets have been accommodated in a stacked state, so as to feed under suction of a suction pad to the succeeding stations (e.g., an exposure station, a developing station, etc.).
When a plurality of the sheets adhere to one another owing to the static electricity or the like, these sheets are to be simultaneously fed to the succeeding station. In the conventional sheet feeding device, the suction pad is normally displaced toward the sheets by a given stroke without taking into consideration the remaining quantity of stacked sheets to be fed. In order to attract an uppermost sheet by the suction pad after the suction pad is pressed against the uppermost sheet, air is forced out from the adjacent sheets, so that the sheets adhere firmly to one another. As a result, a plurality of sheets are simultaneously attracted and held by the suction pad, thus interfering with the following sheet feeding operation of the suction pad in the device. Therefore, the device has to be stopped to correct such malfunction.
In order to avoid such malfunction to be caused in advance, the uppermost sheet attracted by the suction pad is first introduced into a device, comprising a pair of rollers which dislocate in proportion to the thickness of the sheet interposed between the rollers, thereby detecting whether or not a plurality of sheets have been taken out simultaneously. More specifically, the thickness of a single sheet to be inserted between the rollers is set to a thickness detector which detects dislocation of the rollers in proportion to the thickness of the sheet in advance. When two or more sheets are interposed between the rollers, the two rollers are separated from each other beyond the range set in the thickness detector. Since the dislocation is proportional to the thickness of the sheet to be fed it is therefore possible to determine whether or not a plurality of sheets have been fed simultaneously.
In case the thickness detector in the above is used for the detection as to whether or not a plurality of sheets have been fed simultaneously, it is difficult to exactly determine whether a plurality of sheets or a single sheet is fed, since the thickness of each sheet such as a photographic light-sensitive medium is thin (about 0.2 mm) in general. When a plurality of sheets is fed and interposed between the rollers, the rollers damage the sensitive material of each sheet, thereby preventing high quality image recording.